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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Filtering with perfectly correlated measurement noise.

Examination of (radar) Doppler data which are formed by mi1ing the returning microwave signal with a replica of the transmitted signal, counting the cycles of the beat, and sampling the counter at evenly spaced intervals t sub i. It is shown that the amount of information which can be extracted from a set of data may be larger if the associated noise is perfectly correlated than if it is white, and that the use of the white noise assumption in the filter may result in the loss of some of this information.

Reasenberg, R.↗
NASA NTRS1976

Noise measurements in a free-jet, flight simulation facility - Shear layer refraction and facility-to-flight corrections

The conversion of free-jet facility into equivalent flyover results is discussed. The essential problem is to 'calibrate out' the acoustic influence of the outer free-jet shear layer on the measurement, since this is absent in the flight case. Results are presented which illustrate the differences between current simplified models (vortex-sheet and geometric acoustics), and a more complete model based on the Lilley equation. Finally, the use of geometric acoustics for facility-to-flight data conversion is discussed.

Morfey, C. L.↗
NASA NTRS1977

Inlet turbulence and fan noise measured in an anechoic wind tunnel and statically with an inlet flow control device

Turbulence and acoustic measurements were taken in the NASA-Lewis anechoic wind tunnel - a facility which has demonstrated the blade passage tone cutoff phenomena with forward velocity. Turbulence data were taken in a subsonic inlet at various fan speeds under static and forward velocity conditions. A honeycomb/screen flow control device was placed over the inlet during static tests to modify the inflow in an attempt to simulate flight conditions. Acoustic levels of the blade passage tone along with transverse turbulence intensities were reduced with forward velocity. The flow control device reduced the blade passage tone to an intermediate level between those levels associated with static and forward velocity operation.

Shaw, L. M.↗
NASA NTRS1977

Sound separation probes for flowing duct noise measurements

In order to understand the propagation of broadband sound from a device such as a jet engine, it is necessary to make fluctuating pressure measurements in the ducted airstream. However, in a flowing duct, fluctuating pressure energy can be due to both turbulence and sound travelling in the duct. By using the principal that sound waves and turbulent flow pressure perturbations travel at different velocities, a probe has been developed that provides the data necessary to separate the energy due to sound from that due to turbulence. A mini-computer based FFT analysis of the probe measurements provides the overall level of the broadband sound in the duct as well as the spectral distribution of the sound energy.

Moore, M. T.↗
NASA NTRS1961

Aerodynamic Characteristics, Temperature, and Noise Measurements of a Large-Scale External-Flow Jet-Augmented-Flap Model with Turbojet Engines Operating

An investigation has been conducted in the Langley full-scale tunnel on a large-scale model powered by turbojet engines with flattened rectangular nozzles. The wing had 35 deg. sweep of the leading edge, an aspect ratio of 6.5, a taper ratio of 0.31, and NACA 65(1)-412 and 65-408 airfoils at the root and tip. The investigation included measurements of the longitudinal aerodynamic characteristics of the model with half-span and full-span flaps and measurements of the sound pressure and skin temperature on the portions of the lower surface of the wing immersed in the jet flow. The tests were conducted over a range or angles of attack from -8 to 16 deg. for Reynolds numbers from 1.8 x 10(exp 6) to 4.4 x 10(exp 6) and a range of momentum coefficients from 0 to 2.0. In general, the aerodynamic results of this investigation made with a large-scale hot-jet model verified the results of previous investigations with small models powered by compressed-air jets. Although blowing was only done over the inboard portion of the wing, substantial amounts of induced lift were also obtained over the outboard portion of the wing. Skin temperatures were about 340 F and wing heating could be handled with available materials without cooling. Random acoustic loadings on the wing surface were high enough to indicate that fatigue failure from this source would require special consideration in the design of an external-flow jet flap system for an airplane.

Fink, Marvin P.↗
NASA NTRSDate not supplied

Preliminary Analysis of Moog SureFly Electric Motor Noise Measurements

The results of acoustics measurements on the installed and unloaded axial-flux electric motor used on the Moog SureFly® vehicle are presented and compared to previous ground run-up measurements for the vehicle. The directivity of the motor was found to be significantly different than that obtained for much smaller 2 – 4 kW radial flux motors tested previously in the Acoustic Test Laboratory at NASA Glenn. Significant radiation occurred at shaft orders between 17 and 20 and at order 30. Peak radiation levels occurred near the highest speeds expected for the vehicle. There was an indication that some of the tones appearing in the spectra obtained in the previous ground run-up test were associated with the motor.

Urban Air Mobility↗
NASA NTRS1999

An Adaptive Kalman Filter using a Simple Residual Tuning Method

One difficulty in using Kalman filters in real world situations is the selection of the correct process noise, measurement noise, and initial state estimate and covariance. These parameters are commonly referred to as tuning parameters. Multiple methods have been developed to estimate these parameters. Most of those methods such as maximum likelihood, subspace, and observer Kalman Identification require extensive offline processing and are not suitable for real time processing. One technique, which is suitable for real time processing, is the residual tuning method. Any mismodeling of the filter tuning parameters will result in a non-white sequence for the filter measurement residuals. The residual tuning technique uses this information to estimate corrections to those tuning parameters. The actual implementation results in a set of sequential equations that run in parallel with the Kalman filter. Equations for the estimation of the measurement noise have also been developed. These algorithms are used to estimate the process noise and measurement noise for the Wide Field Infrared Explorer star tracker and gyro.

Harman, Richard R.↗
NASA NTRS1980

Acoustical measurement separates core noise and jet noise

Measuring technique discriminates between jet noise and core noise of jet engine. Results of experimentation confirmed that core noise and jet noise can be separated by examining cross-correlation of far-field microphone signals and that crossover point between core noise and jet noise moves toward higher velocities at higher angles with respect to jet axis.

Parthasarathy, S. P.↗